1. Field of the Invention
The present invention relates to an electron microscope and, more particularly, to an electron microscope capable of correcting chromatic aberration and spherical aberration.
2. Description of Related Art
If chromatic aberration (Cc) and spherical aberration (Cs) can be corrected, high-resolution electron microscope imaging is enabled. H. Rose, J. Electron Microsc. 58, 77 (2009), described below, sets forth an aberration-correcting optical system capable of correcting chromatic aberration and spherical aberration at the same time.
However, in an optical system where a chromatic aberration correction and a spherical aberration correction are made at the same time, different properties of aberrations (chromatic and spherical aberrations) are corrected at the same time. Therefore, the electron beam orbit is varied, which is undesirable to one type of aberration correction. Consequently, residual aberrations such as chromatic aberration and star aberrations are produced. This makes it impossible to achieve high-resolution electron microscope imaging.